1. Field of the Invention
This invention relates generally to an industrial truck and, more particularly, to a fork lift truck with a one-piece or multiple-piece vehicle frame, a driver""s cab and one or more components that generate oscillations.
2. Description of the Currently Available Technology
On industrial trucks configured as fork lift trucks, a vehicle frame is located between a rear weight and a lifting platform. The vehicle frame can be formed in one piece or it can consist of a plurality of pieces that are detachably connected to one another. A vertically movable load holding device is fastened to the lifting platform. The forces and moments that act on the lifting platform are supported on the vehicle frame. The vehicle frame is rigidly connected with a rear weight of the fork lift truck, which rear weight is generally in the form of a cast metal block.
Industrial trucks have a whole series of components that generate oscillations that can cause undesirable vibrations and noises. The oscillation-generating components include, for example, an internal combustion engine or a hydraulic system with various hydraulic units and assemblies (e.g. pump, motors, cylinder, lines). Components and assemblies that generate oscillations also include the lifting platform of the industrial truck, which has an inherent tendency to oscillate on account of the weight of the loads lifted and of the lifting platform itself, as well as the wheels, if the industrial truck is traveling on an uneven road surface.
It is particularly important to keep the oscillations caused by the above mentioned components from being transmitted to the driver on board the industrial truck. For this purpose, the prior art mounts the driver""s cab on resilient rubber pads on the vehicle frame. These resilient rubber pads are designed to prevent the transmission of vibrations, including structure-borne noise, into the vicinity of the driver. In this solution of the prior art, the above mentioned components that generate oscillations are generally rigidly connected with the vehicle frame.
This solution of the prior art has the disadvantage that the vehicle frame and the driver""s cab must be formed from separate assemblies, and are therefore complex and expensive to manufacture. An additional disadvantage is that the oscillations that originate from the components in question are transmitted directly to the vehicle frame, as a result of which the vehicle frame is excited to resonant oscillations. These resonant oscillations significantly increase the noise of the industrial truck as perceived by the driver and by persons outside the industrial truck.
Therefore, it is an object of the invention to provide an easily manufactured industrial truck that is characterized by a low level of vibrations and noise during operation.
The invention teaches that, on an industrial truck with a driver""s cab, the driver""s cab has a rigid connection with the vehicle frame and there is at least one elastic damping element between at least one oscillation-generating assembly and a part of the vehicle frame that is connected with the driver""s cab. The driver""s cab can be connected to the vehicle frame by means of threaded fasteners, for example. It is also within the scope of the invention if the driver""s cab is formed at least partly by the vehicle frame.
The effort and expense involved in the manufacture of the industrial truck can be significantly reduced if there need not be any resilient rubber elements between the driver""s cab and the vehicle frame, because it is no longer necessary to separate these two components. The generation of noise in the industrial truck is prevented by the fact that elastic damping elements are located between the respective oscillation-generating assembly and the part of the vehicle frame connected with the driver""s cab, and these damping elements are configured so that they absorb the oscillation frequencies and amplitudes that occur. The transmission of oscillations to the vehicle frame and thus to the driver""s cab can be directly prevented, as a result of which resonances in the vehicle frame are also prevented.
On an industrial truck with a rear weight, the invention teaches that at least one oscillation-generating component is directly or indirectly fastened to the rear weight. The large mass of the rear weight, which is generally made of gray cast iron, cannot be excited to vibrate by the forces generated by the oscillation-generating components. The rear weight therefore transmits neither structure-borne noise nor vibrations to the vehicle frame or to the driver""s cab of the industrial truck.
It is particularly advantageous if the industrial truck has at least one oscillation-generating hydraulic unit that is fastened directly or indirectly by means of an elastic damping element to the part of the vehicle frame that is connected with the driver""s cab. Because of the design of the pump, the flow of hydraulic fluid out of a hydraulic pump always has pressure pulses. These pressure pulses result in a vibration of the hydraulic pump itself, of the valves and lines that are connected with the hydraulic pump, and of the hydraulic users that are connected to it, which are generally in the form of hydraulic motors or hydraulic cylinders. A transmission of these oscillations to the vehicle frame can be prevented if the above mentioned hydraulic units, like the valves and lines, are fastened to the vehicle frame by means of elastic damping elements. It is thereby important that the hydraulic lines do not have any vibration-transmitting connections to the frame, and in particular that there is no direct contact between the hydraulic lines and the frame.
This advantageous effect can also be achieved if the industrial truck has a drive unit that generates vibrations and has at least one hydraulic unit, whereby the hydraulic unit is fastened to a housing that forms a part of the vehicle frame, and this housing is fastened by means of at least one elastic damping element to the part of the vehicle frame that is connected to the driver""s cab. The hydraulic unit of the drive unit can be one or more hydraulic motors, valves and other hydraulic components that are fastened to a common housing. The invention teaches that this housing is connected with the other parts of the vehicle frame by means of elastic damping elements.
If the industrial truck has at least one oscillation-generating lifting platform which is fastened by means of at least one elastic damping element directly or indirectly to the vehicle frame, the oscillations that occur on the lifting platform are also not transmitted to the vehicle frame. In this case, the lifting platform is rotationally connected to the vehicle frame at a first bearing, whereby there is at least one elastic damping element in the vicinity of this bearing between the lifting platform and the vehicle frame. At a second bearing, the lifting platform is connected by means of a hydraulic cylinder with the vehicle frame, whereby between the lifting platform and the hydraulic cylinder and/or between the vehicle frame and the hydraulic cylinder there is at least one elastic damping element.
A particularly good vibration damping action is achieved if at least one oscillation-generating component is fastened by means of at least one elastic damping element to the rear weight. In this arrangement, the transmission of vibrations is prevented on one hand by the damping element and on the other hand by the vibration-damping action of the rear weight as described above. This arrangement is particularly advantageous if the industrial truck has at least one oscillation-generating internal combustion engine which is fastened to the rear weight. It is also possible to fasten an oscillation-generating hydraulic pump to the internal combustion engine. The hydraulic pump and the internal combustion engine thus form a unit and are jointly fastened to the rear weight, for example by means of a damping element.